Handle unreachable code in the dominates functions. This changes users when

needed for correctness, but still doesn't clean up code that now unnecessary
checks for reachability.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153755 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/Dominators.h

@@ -359,8 +359,19 @@ public:
 
   bool dominatedBySlowTreeWalk(const DomTreeNodeBase<NodeT> *A,
                                const DomTreeNodeBase<NodeT> *B) const {
+    // A node trivially dominates itself.
+    if (B == A)
+      return true;
+
+    // An unreachable node is dominated by anything.
+    if (!isReachableFromEntry(B))
+      return true;
+
+    // And dominates nothing.
+    if (!isReachableFromEntry(A))
+      return false;
+
     const DomTreeNodeBase<NodeT> *IDom;
-    if (A == 0 || B == 0) return false;
     while ((IDom = B->getIDom()) != 0 && IDom != A && IDom != B)
       B = IDom;   // Walk up the tree
     return IDom != 0;
@@ -369,10 +380,14 @@ public:
 
   /// isReachableFromEntry - Return true if A is dominated by the entry
   /// block of the function containing it.
-  bool isReachableFromEntry(const NodeT* A) {
+  bool isReachableFromEntry(const NodeT* A) const {
     assert(!this->isPostDominator() &&
            "This is not implemented for post dominators");
-    return dominates(&A->getParent()->front(), A);
+    return isReachableFromEntry(getNode(const_cast<NodeT *>(A)));
+  }
+
+  inline bool isReachableFromEntry(const DomTreeNodeBase<NodeT> *A) const {
+    return A;
   }
 
   /// dominates - Returns true iff A dominates B.  Note that this is not a
@@ -380,10 +395,16 @@ public:
   ///
   inline bool dominates(const DomTreeNodeBase<NodeT> *A,
                         const DomTreeNodeBase<NodeT> *B) {
+    // A node trivially dominates itself.
     if (B == A)
-      return true;  // A node trivially dominates itself.
+      return true;
 
-    if (A == 0 || B == 0)
+    // An unreachable node is dominated by anything.
+    if (!isReachableFromEntry(B))
+      return true;
+
+    // And dominates nothing.
+    if (!isReachableFromEntry(A))
       return false;
 
     // Compare the result of the tree walk and the dfs numbers, if expensive

include/llvm/Analysis/LoopInfo.h

@@ -762,7 +762,8 @@ public:
          InvBlockTraits::child_begin(BB), E = InvBlockTraits::child_end(BB);
          I != E; ++I) {
       typename InvBlockTraits::NodeType *N = *I;
-      if (DT.dominates(BB, N))   // If BB dominates its predecessor...
+      // If BB dominates its predecessor...
+      if (DT.dominates(BB, N) && DT.isReachableFromEntry(N))
           TodoStack.push_back(N);
     }
 

lib/VMCore/Dominators.cpp

@@ -88,8 +88,13 @@ bool DominatorTree::dominates(const Instruction *Def,
   const BasicBlock *UseBB = User->getParent();
   const BasicBlock *DefBB = Def->getParent();
 
-  assert(isReachableFromEntry(DefBB) && isReachableFromEntry(UseBB) &&
-         "We only handle reachable blocks");
+  // Any unreachable use is dominated, even if Def == User.
+  if (!isReachableFromEntry(UseBB))
+    return true;
+
+  // Unreachable definitions don't dominate anything.
+  if (!isReachableFromEntry(DefBB))
+    return false;
 
   // An instruction doesn't dominate a use in itself.
   if (Def == User)
@@ -119,8 +124,13 @@ bool DominatorTree::dominates(const Instruction *Def,
                               const BasicBlock *UseBB) const {
   const BasicBlock *DefBB = Def->getParent();
 
-  assert(isReachableFromEntry(DefBB) && isReachableFromEntry(UseBB) &&
-         "We only handle reachable blocks");
+  // Any unreachable use is dominated, even if DefBB == UseBB.
+  if (!isReachableFromEntry(UseBB))
+    return true;
+
+  // Unreachable definitions don't dominate anything.
+  if (!isReachableFromEntry(DefBB))
+    return false;
 
   if (DefBB == UseBB)
     return false;

unittests/CMakeLists.txt

@@ -139,6 +139,7 @@ set(VMCoreSources
   VMCore/PassManagerTest.cpp
   VMCore/ValueMapTest.cpp
   VMCore/VerifierTest.cpp
+  VMCore/DominatorTreeTest.cpp
   )
 
 # MSVC9 and 8 cannot compile ValueMapTest.cpp due to their bug.

unittests/VMCore/DominatorTreeTest.cpp

@@ -0,0 +1,195 @@
+#include "llvm/Instructions.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/Module.h"
+#include "llvm/PassManager.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Assembly/Parser.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace llvm {
+  void initializeDPassPass(PassRegistry&);
+
+  namespace {
+    struct DPass : public FunctionPass {
+      static char ID;
+      virtual bool runOnFunction(Function &F) {
+        DominatorTree *DT = &getAnalysis<DominatorTree>();
+        Function::iterator FI = F.begin();
+
+        BasicBlock *BB0 = FI++;
+        BasicBlock::iterator BBI = BB0->begin();
+        Instruction *Y1 = BBI++;
+        Instruction *Y2 = BBI++;
+        Instruction *Y3 = BBI++;
+
+        BasicBlock *BB1 = FI++;
+        BBI = BB1->begin();
+        Instruction *Y4 = BBI++;
+
+        BasicBlock *BB2 = FI++;
+        BBI = BB2->begin();
+        Instruction *Y5 = BBI++;
+
+        BasicBlock *BB3 = FI++;
+        BBI = BB3->begin();
+        Instruction *Y6 = BBI++;
+        Instruction *Y7 = BBI++;
+
+        BasicBlock *BB4 = FI++;
+        BBI = BB4->begin();
+        Instruction *Y8 = BBI++;
+        Instruction *Y9 = BBI++;
+
+        // Reachability
+        EXPECT_TRUE(DT->isReachableFromEntry(BB0));
+        EXPECT_TRUE(DT->isReachableFromEntry(BB1));
+        EXPECT_TRUE(DT->isReachableFromEntry(BB2));
+        EXPECT_FALSE(DT->isReachableFromEntry(BB3));
+        EXPECT_TRUE(DT->isReachableFromEntry(BB4));
+
+        // BB dominance
+        EXPECT_TRUE(DT->dominates(BB0, BB0));
+        EXPECT_TRUE(DT->dominates(BB0, BB1));
+        EXPECT_TRUE(DT->dominates(BB0, BB2));
+        EXPECT_TRUE(DT->dominates(BB0, BB3));
+        EXPECT_TRUE(DT->dominates(BB0, BB4));
+
+        EXPECT_FALSE(DT->dominates(BB1, BB0));
+        EXPECT_TRUE(DT->dominates(BB1, BB1));
+        EXPECT_FALSE(DT->dominates(BB1, BB2));
+        EXPECT_TRUE(DT->dominates(BB1, BB3));
+        EXPECT_FALSE(DT->dominates(BB1, BB4));
+
+        EXPECT_FALSE(DT->dominates(BB2, BB0));
+        EXPECT_FALSE(DT->dominates(BB2, BB1));
+        EXPECT_TRUE(DT->dominates(BB2, BB2));
+        EXPECT_TRUE(DT->dominates(BB2, BB3));
+        EXPECT_FALSE(DT->dominates(BB2, BB4));
+
+        EXPECT_FALSE(DT->dominates(BB3, BB0));
+        EXPECT_FALSE(DT->dominates(BB3, BB1));
+        EXPECT_FALSE(DT->dominates(BB3, BB2));
+        EXPECT_TRUE(DT->dominates(BB3, BB3));
+        EXPECT_FALSE(DT->dominates(BB3, BB4));
+
+        // BB proper dominance
+        EXPECT_FALSE(DT->properlyDominates(BB0, BB0));
+        EXPECT_TRUE(DT->properlyDominates(BB0, BB1));
+        EXPECT_TRUE(DT->properlyDominates(BB0, BB2));
+        EXPECT_TRUE(DT->properlyDominates(BB0, BB3));
+
+        EXPECT_FALSE(DT->properlyDominates(BB1, BB0));
+        EXPECT_FALSE(DT->properlyDominates(BB1, BB1));
+        EXPECT_FALSE(DT->properlyDominates(BB1, BB2));
+        EXPECT_TRUE(DT->properlyDominates(BB1, BB3));
+
+        EXPECT_FALSE(DT->properlyDominates(BB2, BB0));
+        EXPECT_FALSE(DT->properlyDominates(BB2, BB1));
+        EXPECT_FALSE(DT->properlyDominates(BB2, BB2));
+        EXPECT_TRUE(DT->properlyDominates(BB2, BB3));
+
+        EXPECT_FALSE(DT->properlyDominates(BB3, BB0));
+        EXPECT_FALSE(DT->properlyDominates(BB3, BB1));
+        EXPECT_FALSE(DT->properlyDominates(BB3, BB2));
+        EXPECT_FALSE(DT->properlyDominates(BB3, BB3));
+
+        // Instruction dominance in the same reachable BB
+        EXPECT_FALSE(DT->dominates(Y1, Y1));
+        EXPECT_TRUE(DT->dominates(Y1, Y2));
+        EXPECT_FALSE(DT->dominates(Y2, Y1));
+        EXPECT_FALSE(DT->dominates(Y2, Y2));
+
+        // Instruction dominance in the same unreachable BB
+        EXPECT_TRUE(DT->dominates(Y6, Y6));
+        EXPECT_TRUE(DT->dominates(Y6, Y7));
+        EXPECT_TRUE(DT->dominates(Y7, Y6));
+        EXPECT_TRUE(DT->dominates(Y7, Y7));
+
+        // Invoke
+        EXPECT_TRUE(DT->dominates(Y3, Y4));
+        EXPECT_FALSE(DT->dominates(Y3, Y5));
+
+        // Phi
+        EXPECT_TRUE(DT->dominates(Y2, Y9));
+        EXPECT_FALSE(DT->dominates(Y3, Y9));
+        EXPECT_FALSE(DT->dominates(Y8, Y9));
+
+        // Anything dominates unreachable
+        EXPECT_TRUE(DT->dominates(Y1, Y6));
+        EXPECT_TRUE(DT->dominates(Y3, Y6));
+
+        // Unreachable doesn't dominate reachable
+        EXPECT_FALSE(DT->dominates(Y6, Y1));
+
+        // Instruction, BB dominance
+        EXPECT_FALSE(DT->dominates(Y1, BB0));
+        EXPECT_TRUE(DT->dominates(Y1, BB1));
+        EXPECT_TRUE(DT->dominates(Y1, BB2));
+        EXPECT_TRUE(DT->dominates(Y1, BB3));
+        EXPECT_TRUE(DT->dominates(Y1, BB4));
+
+        EXPECT_FALSE(DT->dominates(Y3, BB0));
+        EXPECT_TRUE(DT->dominates(Y3, BB1));
+        EXPECT_FALSE(DT->dominates(Y3, BB2));
+        EXPECT_TRUE(DT->dominates(Y3, BB3));
+        EXPECT_FALSE(DT->dominates(Y3, BB4));
+
+        EXPECT_TRUE(DT->dominates(Y6, BB3));
+
+        return false;
+      }
+      virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+        AU.addRequired<DominatorTree>();
+      }
+      DPass() : FunctionPass(ID) {
+        initializeDPassPass(*PassRegistry::getPassRegistry());
+      }
+    };
+    char DPass::ID = 0;
+
+
+    Module* makeLLVMModule(DPass *P) {
+      const char *ModuleStrig =
+        "declare i32 @g()\n" \
+        "define void @f(i32 %x) {\n" \
+        "bb0:\n" \
+        "  %y1 = add i32 %x, 1\n" \
+        "  %y2 = add i32 %x, 1\n" \
+        "  %y3 = invoke i32 @g() to label %bb1 unwind label %bb2\n" \
+        "bb1:\n" \
+        "  %y4 = add i32 %x, 1\n" \
+        "  br label %bb4\n" \
+        "bb2:\n" \
+        "  %y5 = landingpad i32 personality i32 ()* @g\n" \
+        "          cleanup\n" \
+        "  br label %bb4\n" \
+        "bb3:\n" \
+        "  %y6 = add i32 %x, 1\n" \
+        "  %y7 = add i32 %x, 1\n" \
+        "  ret void\n" \
+        "bb4:\n" \
+        "  %y8 = phi i32 [0, %bb2], [%y4, %bb1]\n"
+        "  %y9 = phi i32 [0, %bb2], [%y4, %bb1]\n"
+        "  ret void\n" \
+        "}\n";
+      LLVMContext &C = getGlobalContext();
+      SMDiagnostic Err;
+      return ParseAssemblyString(ModuleStrig, NULL, Err, C);
+    }
+
+    TEST(DominatorTree, Unreachable) {
+      DPass *P = new DPass();
+      Module *M = makeLLVMModule(P);
+      PassManager Passes;
+      Passes.add(P);
+      Passes.run(*M);
+    }
+  }
+}
+
+INITIALIZE_PASS_BEGIN(DPass, "dpass", "dpass", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_END(DPass, "dpass", "dpass", false, false)

unittests/VMCore/Makefile

@@ -9,7 +9,7 @@
 
 LEVEL = ../..
 TESTNAME = VMCore
-LINK_COMPONENTS := core support target ipa
+LINK_COMPONENTS := core support target ipa asmparser
 
 include $(LEVEL)/Makefile.config
 include $(LLVM_SRC_ROOT)/unittests/Makefile.unittest